An Experimental Evaluation of Two Potential Improvements for 3D Laser Vibrometer Based Operational Modal Analysis

The use of scanning laser doppler vibrometers (SLDV) is common practice in the context with experimental modal analysis. In recent years, commercial 3D SLDV have been developed, where three laser heads simultaneously point to the same measuring point and an input reference signal is used to combine the results of consecutive records. If the input reference signal is replaced by an additional output reference signal, an operational modal analysis (OMA) can be performed. However, in this case the use of single-point measurements may lead to difficulties identifying certain vibrational modes. Two improvements to reduce these issues were developed in this study: the application of pre-estimation multi-setup merging methods and the use of multi-point measurements with post-estimation coordinate transformation. An enhancement for the application of OMA methods is shown in both cases. In this context there are different possibilities to obtain output reference signals: a) from additional accelerometers or vibrometers and b) from the scan heads of the 3D SLDV itself. Their suitability is investigated in terms of data acqusition, modal analysis and multi-setup merging. Additionally, the feasibility of a “no-reference” measurement is shown. The developed methods have been applied to experimental data using the stochastic subspace identification (cov/ref) and three multi-setup merging methods.